1. Field of the Invention
The present invention relates to field-programmable analog arrays and, more particularly, to programming large-scale field-programmable analog arrays for use in analog circuitry.
2. Description of Related Art
Even in today's world of digital electronics, it is often desirable, or even necessary to use and process analog signals. For example, most audio files, while typically stored in digital form such as MP3s and compact disks, must be converted to an analog signal in order to be heard through a speaker. Additionally, many other types of equipment depend on analog signals.
Often it is desirable to process the analog signals, and it may even be desirable to store the analog signals electronically. Currently, circuits used for analog processing and storage have a long development cycle and are typically large. It would be useful to create analog circuitry that allows for flexible analog design in a compact package.
Generally, a field-programmable analog array (FPAA) is a programmable integrated circuit capable of implementing an enormous range of analog signal processing functions. The FPAA typically comprises a computational analog block (CAB) and an interconnect network, such that one FPAA may be distinguished from another by these two components. For the interconnect structure, an FPAA is most commonly connected by metal-oxide semiconductor (MOS) transistor switches driven by digital memory. Conventional alternatives to pass-FETs and transmission gates (T-gates) often provide increased bandwidth and include Gm-C amplifiers, 4-transistor transconductors, and current conveyors. Unfortunately, each of these alternatives trade area for improved switch characteristics and require an additional physical memory element for maintaining connectivity within the FPAA.
As the industry pushes toward shorter design cycles for analog integrated circuits, the need for an efficient and effective FPAA becomes paramount. Indeed, the role of analog integrated circuits in modern electronic systems remains important, even with the advent of digital circuits. Analog systems, for example, are often used to interface with digital electronics in applications such as biomedical measurements, industrial process control, and analog signal processing. More importantly, analog solutions may become increasingly competitive with digital circuits for applications requiring dense, low-power, and high-speed signal processing.
FPAAs provide a method for rapidly prototyping analog systems. FPAAs have been of interest for some time, but historically, these devices have had very few programmable elements and limited interconnect capabilities, making them limited in their usefulness and versatility. Currently available commercial and academic FPAAs are typically based on operational amplifiers (or other similar analog primitives) with only a few computational elements per chip. While specific architectures vary, their small sized and often restrictive interconnect designs leave current FPAAs limited in functionality and flexibility. For FPAAs to enter the realm of large-scale reconfigurable devices, such as modern field-programmable gate arrays (FPGAs), new technologies must be explored to provide area-efficient accurately programmable analog circuitry that may be easily integrated into a larger digital/mixed-signal system.
Indeed, the growing demand for complex information processing on portable devices has motivated significant research in the design of power efficient signal processing systems. One method for achieving low-power designs is to move processing on system inputs from the digital processor to analog hardware situated before the analog-to-digital converter (ADC). For analog systems to be desirable to digital signal processing engineers, however, the analog systems need to provide a significant advantage in terms of size and power and yet still remain relatively easy to use and integrate into a larger digital system. Reconfigurable analog arrays, dubbed field-programmable analog arrays (FPAAs), can speed the transition of systems from digital to analog by providing the ability to rapidly implement advanced, low-power signal processing systems, particularly signal processing utilizing programmable analog techniques.
Gene's law postulates that the power consumption in digital signal processing microprocessors, as measured in milliwatts per million multiply-accumulate (mW/MMAC) operations, is halved about every 18 months. These advances largely follow Moore's law, and they are achieved by using decreased feature size and other refinements, such as intelligent clock gating. Myriad applications only dreamed of a few years ago are possible because of these gains, and they have increased the demand for more advanced signal processing systems. Unfortunately, a problem looms on the horizon: the power consumption of the ADC does not follow Gene's law and will soon dominate the total power budget of digital systems. While ADC resolution has been increasing at roughly 1.5 bits every five years, the power performance has remained the same, and soon, physical limits will further slow progress. Most current signal processing systems that generate digital output place the ADC as close to the analog input signal as possible to take advantage of the computational flexibility available in digital processors.
For digital systems, an intermediate frequency signal processing system requires the use of an array of digital signal processors operating in parallel to meet desired speed requirements. This is a power intensive approach and makes use of certain communication schemes impractical in portable applications. The front-end analog-to-digital converter and back-end digital-to-analog converter required in these systems become expensive when the signal is of a wideband nature and high resolution is desired. One of the building blocks that would enable multiple analog signal processing applications is a programmable analog waveform generator. Unfortunately, no such analog waveform generator exists.
What is needed, therefore, is a system and method of effectively programming a floating-gate array, such as a large-scale FPAA, utilizing programmable floating-gate transistors as switches and/or computational elements. Further, what is needed is a system and method for building larger, more flexible FPAAs, so that reconfigurable analog devices will become more analogous to today's high-density field programmable gate array (FPGA) architectures. Moreover, what is needed is a programmable arbitrary waveform generator to enable implementation of more complex analog signal processing applications. It is to such systems and methods that the present invention is primarily directed.